An object is to provide a process for producing the compound of formula 1 in higher yield by the ring-opening addition reaction of epoxytriazole with amine under mild conditions without using a large excess of 4-methylenepiperidine. The process for producing (2 R ,3 R )-2-(2,4-difluorophenyl)-3-(4-methylenepiperidin-1-yl)-1-(1 H -1,2,4-triazol-1-yl)butan-2-ol or an acid addition salt thereof comprises reacting (2 R ,3 S )-2-(2,4-difluorophenyl)-3-methyl-2-[(1 H -1,2,4-triazol-1-yl)methyl]oxirane with an acid addition salt of 4-methylenepiperidine in a reaction solvent in the presence of a hydroxide of an alkali metal or an alkaline earth metal selected from the group consisting of lithium, sodium, calcium, and strontium, or a hydrate thereof.
